The invention disclosed herein resides in the art of antiskid control circuitry for operation in the braking systems of wheeled vehicles. Particularly, the invention comprises a circuit for implementation between wheel speed transducers associated with the wheels of an aircraft and a valve or valves for braking the wheels in such a manner as to optimize braking efficiency. While the invention discussed hereinafter is with respect to an aircraft having two braked wheels, both wheels being controlled by the same valve, it will be understood that such need not be the case and that the techniques and circuitry described are equally applicable to aircraft or other vehicles having any number of braked wheels and which may be controlled independently of each other.
Heretofore in the art, a vast number of antiskid systems have been developed and utilized. Such systems have generally incorporated a squat switch and associated circuitry to assure that brake pressure is dumped upon touchdown. However, no known systems provide for brake pressure being enabled a predetermined time period after touchdown or upon the wheels reaching a predetermined rotational speed, whichever occurs first.
In antiskid systems, the prior art teaches the utilization of modulators which are unaffected by small perturbations of the wheel deceleration signals above a predetermined deceleration threshold level, but not exceeding an inherent modulator threshold level. Hence, not all changes in wheel deceleration above the deceleration threshold affect the modulator output. Further, such deceleration signals have been generated by deceleration detectors which fail to provide fast response to changes in wheel deceleration and which are generally complex with respect to threshold and gain calibration.
Other inherent problems in the prior art include but a single system gain which cannot be automatically adjusted to compensate for the severity of skids experienced, or for a decrease in runway coefficient over a prolonged period of time. Further, in certain known systems, the discharge rate of the modulator capacitor is exponential, resulting in a nonlinear operation of the modulator, and there is no provision for means to adjust the modulator discharge rate when no skids are experienced for a particular period of time.
Any attempts to overcome the problems inherent in the prior art as set forth above have generally been both complex in nature and expensive in cost and, hence, have not been suitable for implementation in the industry.